Method and apparatus for drying a load of moist fibrous material, particularly a load of laundry

ABSTRACT

A method and an apparatus is described for drying a load of moist fibrous material, particularly a load of laundry washed and placed in a washer/drier machine or a clothes drier, wherein a closed-circuit flow of superheated steam at 102-180° C. and substantially at atmospheric pressure is passed through the load of fibrous material. The method is characterized in that, prior to the superheated steam drying step, the air in the closed circuit is flushed therefrom with steam.

CROSS REFERENCE TO RELATED APPLICATION

This is the 35 USC 371 National Stage of International applicationPCT/FR97/00408 filed on Mar. 7, 1997, which designated the United Statesof America.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for drying aload of moist fibrous material, particularly a load of laundry washedand placed in a washer/drier machine or a clothes drier.

BACKGROUND OF THE INVENTION

In heretofore known clothes driers, various hot fluids have been used asdrying means. In particular, hot air has been employed, blown inside aclothes drier, at a temperature of the order of 120° C., but such amethod of drying presents the drawback of being particularly long and ofconsuming a considerable amount of energy. To overcome this drawback, ithas already been envisaged to use, for drying laundry, superheated steamplaced in forced circulation through an enclosure containing the laundryto be dried.

Document WO No. 89/04392 discloses a method and an apparatus for drying,a load of laundry contained in an enclosure, by means of superheatedsteam. The superheated steam is made to circulate through the enclosure,in closed circuit, by means of a fan mounted upstream of the enclosureand downstream of a source of heat so as to deliver into the enclosurethe steam evaporating from the laundry. At the beginning of a dryingcycle, the air contained in the enclosure is delivered via a vent towhich a condenser is connected in by-pass.

Document EP-A-0 026 707 discloses a method and an apparatus for drying,in which the drying cycle comprises a first spinning phase in whichthere is circulated through an enclosure, containing the material to bedried, steam produced by an independent steam generator, and a secondphase in which there is circulated, by means of a fan connected upstreamof the enclosure, the steam evaporated from the moist material, thissteam passing through a superheater. A condenser is connected in by-passat the outlet of the enclosure containing the moist material.

SUMMARY OF THE INVENTION

The present invention relates to improvements in the known methods andapparatus, making it possible in particular to reduce the overall timefor drying a load of fibrous material and to considerably reduce thecost of the drying apparatus.

To that end, this method of drying a load of moist fibrous material,particularly a load of moist laundry after washing, in which there ispassed through the load of fibrous material, in closed circuit,superheated steam at a temperature included between 102° and 180° C. andsubstantially at atmospheric pressure, characterized in that itcomprises, prior to the superheated steam drying step, a previous phaseof flushing the air present in the closed circuit by means of steam.

The invention also has for an object an apparatus for drying a load ofmoist fibrous material, particularly a load of moist laundry afterwashing, comprising an enclosure in which is housed the load of moistlaundry, a steam generator, a superheater, a condenser, and a fan forcirculating in a principal pipe in closed circuit, superheated steam ata temperature ranging from 102° C. to 180° C., through the enclosure andthe load of moist fibrous material that it contains, characterized inthat the fan provided to ensure circulation of the steam is constitutedby an exhauster fan connected, on the principal pipe, downstream of theoutlet of the enclosure, in order to create a slight depression in thisenclosure, the condenser and the superheater are connected in seriesupstream of the enclosure, the principal pipe is connected, towards thedelivery of the fan, on the one hand to a first electrovalve forcommunication with the open air, connected in by-pass, and on the otherhand to a second electrovalve connected in series and the steamgenerator is connected to the principal pipe, downstream of the secondelectrovalve, via a third electrovalve.

The method and the apparatus for drying according to the invention offerthe advantage of enabling the apparatus to be simplified. In effect, theprior rinsing of the closed circuit of its air, by means of the steam,before the drying phase proper, allows the apparatus to operate atatmospheric pressure and the temperautre of the steam inside the dryingenclosure is therefore obligatorily always greater than 100° C. fornormal atmospheric pressure. The cost of a clothes drier according tothe invention may thus be considerably reduced as it is not necessary touse sophisticated sealing devices (water-tight seals, etc . . . ).

BRIEF DESCRIPTION OF THE DRAWINGS

A form of embodiment of the present invention will be describedhereinafter by way of a non-limiting example with reference to theaccompanying drawings, of which the single FIGURE is a diagram of anapparatus for drying laundry by means of superheated steam, according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

The drying apparatus comprises an enclosure 1 in which is placed theload of fibrous material to be dried which, within the framework of thepresent description, will be considered as being moist laundry, as afterwashing. The enclosure 1 may be constituted by a drum rotated bymechanical drive and adapted to rotate alternately in the twodirections, so as to move the laundry. The enclosure 1 may also beconstituted by a clothes drier in which the pieces of laundry areimmobile, being suspended in an appropriate manner. The enclosure 1 mayalso be of the type with continuous circulation of pieces of laundry,from an inlet of the enclosure 1 to the outlet.

The enclosure 1 is connected to an outlet conduit 2 in which is housed aturbo exhauster fan 3 creating a depression in the enclosure 1 when itis switched on. The outlet conduit 2 is connected to a principal pipe 4connected in a closed principal circuit with, the enclosure 1 andconnected to that end to an inlet orifice of this enclosure. Thisprincipal pipe 4 is intended for the circulation, in the closedprincipal circuit, of superheated steam and/or air, as will be specifiedhereinafter. To pipe 4 there is connected, downstream of the fan 3, anelectrovalve 5 also forming a valve for communication with the open air,calibrated for example at a pressure of 1.05 bar absolute. Downstream ofthe point of connection of the electrovalve 5 there is connected anotherelectrovalve 6, in series in the pipe 4, and downstream of thiselectrovalve 6 is branched in by-pass another electrovalve 7 connectedto the upper part of a steam generator 8. On the pipe connecting theelectrovalve 7 to the steam generator 8 there is connected a safetyvalve 9 calibrated at a pressure of 1.2 bar absolute for example. Thesteam generator 8 is connected to a source of water via a valve 11 andit comprises an electrical heating device 12 for provoking thevaporization of the water contained in the generator 8.

On pipe 4 is connected in series, downstream of the steam generator 8, asteam condenser 13 provided with an air or water cooling circuit 14. Thecondenser 13 is adjusted so that the temperature of condensation isalways slightly greater than the temperature of saturation correspondingto atmospheric pressure, i.e. 100° C. for a normal atmospheric pressure.The condenser 13 contains a float 15 connected to a level sensor 16detecting the level of water in a condensate recuperator 17 located inthe lower part of the condenser 13. Below the condensate recuperator 17there is located a condensate tank 18.

After the condenser 13, i.e. downstream in the direction of circulationof the steam, the principal pipe 4 in the closed principal circuitcomprises an electrovalve 19 connected in series. The pipe 4 is thenconnected to the inlet of a superheater 21. This superheater 21comprises an electrical heating circuit 22 producing superheating of thesteam to a temperature ranging from 102° C. to 180° C. Upstream of thesuperheater 21, an electrovalve 23 is connected to pipe 4 to allow anadmission of air in the principal circuit.

According to a variant, the steam generator 8 might be associated withthe superheater 21, forming one and the same unit supplying superheatedsteam from liquid water.

The apparatus may also comprise a dehydrator 24 connected in parallel onthe electrovalve 19 and connected to the principal pipe 4, on eitherside of the electrovalve 19, by two electrovalves 25 and 26. Thedehydrator 24 comprises a matrix of dehydrating material, capable ofabsorbing or adsorbing the steam and able to be regenerated by heatingby means of an electrical heating device 27.

The temperature of the fluid (steam and/or air) flowing in the principalcircuit is monitored by means of two temperature probes 28, 29 mountedrespectively at the inlet and at the outlet of the enclosure 1, in orderto detect the inlet temperature T1 and outlet temperature T2 of thesteam passing through the enclosure 1.

The various electrovalves 5, 6, 7, 11, 19, 23, 25, 26, the heatingdevice 12 of the steam generator 8, the heating circuit 22 of thesuperheater 21 and the heating device 27 of the dehydrator 24, areconnected to a general automatic control device 31 which adjusts thefunctioning of the apparatus. This device 31 is also connected to theturbo exhauster 3 to control start and stop of this fan. The device 31also receives information coming from the level sensor 16 of thecondenser 13 and from the temperature probes 28 and 29.

The functioning of the apparatus carrying out the method of dryingaccording to the present invention will now be described.

In the case of a discontinuous method, i.e. of drying of successivebatches of laundry, the method of drying comprises a first phase duringwhich the moist air normally present in the principal circuit isreplaced by steam, superheated or not, circulating in open circuit. Thismoist air is located in the enclosure 1 and the rate of humidity and thetemperature of this air are variable. At the beginning of the firstphase, the automatic control device 31 provokes several simultaneousoperations, namely the switching on of the steam generator 8, so as toproduce in this generator steam at a temperature of 102° C., the openingof the electrovalves 5 and 7, the closure of the electrovalve 6, theswitching on of the fan 3 and possibly the switching on of thesuperheater 21. The fan 3 creates a depression inside the enclosure 21,so that the steam produced by the steam generator 8 flows successivelythrough the open electrovalve 7, the principal pipe 4, the condenser 13,of which the external cooling system is stopped during this phase, andthe open electrovalve 19 and it is introduced in the superheater 21 thenin the enclosure 1 and this steam flushes out the air contained in theprincipal circuit and in the enclosure 1, this air being delivered tothe outside, jointly with the steam, through the open electrovalve 5.This first phase of flushing and of replacement of the moist air bysteam, possibly superheated, lasts a predetermined time which may easilybe calculated from the known volume of the apparatus. At the end of thisfirst phase, only steam, superheated or not, circulates in the principalpipe 4, at atmospheric pressure, and the principal circuit no longercontains air. At that moment, the automatic control device 31 provokesclosure of the electrovalves 5, 7, the stop of the steam generator 8 andthe opening of electrovalve 6, this establishing a closed circuit forthe subsequent circulation of steam.

The method of drying then passes to a second phase or principal phaseduring which the laundry contained in the enclosure 1 is dried by thesuperheated steam and the water extracted from the laundry is condensedin continuous manner in the condenser 13. At the beginning of thissecond phase, the automatic control device 31 provokes operation of thesuperheater 21, if it were not already operating during the first phaseof flushing of the air. During the principal phase of drying, the fan 3continues to rotate, producing the circulation in closed circuit of thesteam which is superheated in the superheater 21. In the condenser 13, apart of the steam condenses and the condenser thus withdraws aprogressively increasing quantity of water from the closed circuit,allowing optimal functioning of the clothes drier. The power of thecondenser 13 is servo-controlled by the outlet temperature T2 of thesteam of the enclosure 1. In fact, as drying progresses, the flow rateof water extracted from the laundry decreases, the temperature T1increases and the power of the condenser 13 decreases. The level of thecondensate collected in the recuperator 17 is detected by the float 15acting on the level sensor 16. This sensor 16 makes it possible, jointlywith the temperature probes 28 and 29, to determine the end of drying.In other words, when the level sensor 16 detects that the level of thecondensed water in the condensate recuperator 17 virtually no longervaries and the temperature probes 28 and 29 indicate that the inlettemperature T1 and outlet temperature T2 are virtually identical, thismeans that the laundry has attained its final drying point. At thatmoment, the automatic control device 31 automatically stops the dryingcycle.

The principal phase of drying with the aid of superheated steam maypossibly be followed by a third phase of drying by means of dry air.

What is claimed is:
 1. Method of drying a load of moist fibrous laundry material after washing, contained in a circuit containing moist air, the method comprising the following two successive phases:a first phase of flushing and replacement of the moist air present in the circuit with steam whereby air is withdrawn from the circuit and released to the atmosphere; and a second drying phase of passing superheated steam at a temperature ranging between 102° C.-180° C. and substantially at atmospheric pressure through the load of fibrous laundry material, in closed circuit.
 2. Apparatus for drying a load of moist fibrous material, comprising:an enclosure for housing the load of moist fibrous material, said enclosure having an outlet and an inlet connected in a closed circuit containing moist air with a principal pipe; heating means for producing steam, connected to said principal pipe upstream of the inlet of said enclosure; said heating means being structured and arranged to produce a) steam during a first phase of flushing and replacement of the moist air by steam, and b) superheated steam at a temperature ranging from 102° C. to 180° C. and substantially at atmospheric pressure during a subsequent second drying phase; an exhaust fan connected on said principal pipe for circulating steam during the first phase of flushing the moist air, and thereafter for circulating superheated steam during the second drying phase through the principal pipe and the enclosure; selective communication means operatively associated with the circuit for venting to the outside, during said first phase, the air content in the moist air; and condensing means connected to said principal pipe for condensing a part of the steam.
 3. The apparatus according to claim 2, wherein said heating means comprise a steam generator and a superheater connected to said principal pipe upstream of the inlet of said enclosure, and said selective communication means comprise:a first electrovalve for communication with ambient air; a second electrovalve connected in series on said principal pipe downstream of the fan and downstream of the enclosure; and a third electrovalve for communication with the steam generator; said first electrovalve being connected in by-pass to said principal pipe downstream of the fan and upstream of the second electrovalve; and said third electrovalve being connected in by-pass to said principal pipe downstream of the second electrovalve.
 4. The apparatus according to claim 3, wherein said condensing means comprise a condensate recuperator and a level sensor for detecting condensed water collected within said condensate recuperator.
 5. The apparatus according to claim 3, wherein the principal pipe comprises a fourth electrovalve connected in series on the principal pipe and a dehydrator connected in parallel to the principal pipe, on either side of the fourth electrovalve, by fifth and sixth electrovalves; the dehydrator comprising a matrix of dehydrating material which may be regenerated by heating with an electrical heating device.
 6. The apparatus according to claim 3, further comprising two temperature probes mounted respectively at the inlet and at the outlet of the enclosure for detecting temperatures (T1) and (T2) of the superheated steam passing respectively through the inlet and outlet of the enclosure.
 7. The apparatus according to claim 3, further comprising a seventh electrovalve connected on said principal pipe upstream of the superheater for introducing air into the principal pipe.
 8. The apparatus according to claim 3, further comprising first and second temperature probes for detecting temperatures (T1) and (T2) at the inlet and the outlet of the superheated steam, and an automatic control device operatively connected to the heating means and to the first and second temperature probes for controlling the two successive phases of flushing of the air and of drying as a function of the detected temperatures.
 9. The apparatus according to claim 8, wherein the automatic control device is connected to the first, second and third electrovalves.
 10. The apparatus according to claim 8, further comprising a sensor for sensing the level of condensate in the condensing means, said sensor being operatively connected to the automatic control device for controlling the two successive phases of flushing of the air and of drying as a function of the level of the condensate. 